1. Field of the Invention
This invention relates to an image forming method and an image forming apparatus intended to prevent deterioration of an image resulting from various kinds of ills and failures in the image forming process.
2. Description of Related Art
In a long-time use of a copying machine, such inconveniences may come to appear that a photosensitive body is charged not properly or an adequate exposure cannot be obtained. This is because of the contamination of an electrostatic wire, an electrostatic grid or the like of an electrostatic charger, or the surface deterioration of the electrostatic wire or unevenness of characteristics of the photosensitive body, and also the deterioration of an exposure lamp of an optical system or the contamination of mirrors and lenses, etc. causes the inadequate exposure referred to above. Moreover, these inconveniences undesirably result in a blur of a copied image or a so-called background fog with excessive toners adhered. As such, the assignee of this invention has proposed an apparatus to change the quantity of exposure light (for example, as disclosed in the published specification of Japanese Patent Application Laid-Open No. 63-223762). With this apparatus, a reference latent image is formed on a photosensitive body and then developed into a toner image before a document is copied. Thereafter, the voltage of an exposure lamp is automatically adjusted in response to the measured density of the developed toner image and the density of the document. Incidentally, it is general for the apparatus that a density sensor is fixedly provided, for example, at the center in an elongated direction of a photosensitive drum.
When improper charging or improper exposure occurs in such apparatus as above at the point other than where the density is measured, the copied image cannot have proper density. Because the quantity of exposure light at the point where the improper charging or exposure actually occurs cannot be corrected properly even if the light exposure is arranged to be changed in response to the density of the toner image measured at the fixed measuring point. The copying apparatus of this kind cannot avoid the background fog by itself, thereby requiring an operator to set the quantity of exposure light again properly and to copy again in order to obtain a copy without a background fog. Therefore, the prior art copying apparatus not only gives annoyance to the operator, but wastes copying papers and toners.
In the case where the toner image is formed all over the photosensitive body and the density of the toner image is measured, it does not match an economical viewpoint to consume the toners for the toner image formed at the points other than the measured point.